Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 1 Chapter 41 Microbiology of Food

Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 2 Microorganism Growth in Foods Figure 41.1

Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 3 Intrinsic Factors composition pH presence and availability of water oxidation-reduction potential –altered by cooking physical structure presence of antimicrobial substances

Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 4 Composition and pH putrefaction –proteolysis and anaerobic breakdown of proteins, yielding foul-smelling amine compounds pH impacts make up of microbial community and therefore types of chemical reactions that occur when microbes grow in food

Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 5 Water availability in general, lower water activity inhibits microbial growth water activity lowered by: –drying –addition of salt or sugar osmophilic microorganisms –prefer high osmotic pressure xerophilic microorganisms –prefer low water activity

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7 Physical structure grinding and mixing increase surface area and distribute microbes –promotes microbial growth outer skin of vegetables and fruits slows microbial growth

Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 8 Antimicrobial substances coumarins – fruits and vegetables lysozyme – cow’s milk and eggs aldehydic and phenolic compounds – herbs and spices allicin – garlic polyphenols – green and black teas

Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 9 Extrinsic Factors temperature –lower temperatures retard microbial growth relative humidity –higher levels promote microbial growth atmosphere –oxygen promotes growth –modified atmosphere packaging (MAP) use of shrink wrap and vacuum technologies to package food in controlled atmospheres

Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 10 Microbial Growth and Food Spoilage food spoilage –results from growth of microbes in food alters food visibly and in other ways, rendering it unsuitable for consumption –involves predictable succession of microbes –different foods undergo different types of spoilage processes –toxins are sometimes produced algal toxins may contaminate shellfish and finfish

Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 11 Figure 41.2

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Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 13 Toxins ergotism –toxic condition caused by growth of a fungus in grains aflatoxins –carcinogens produced in fungus- infected grains and nut products fumonisins –carcinogens produced in fungus- infected corn

Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 14 Figure 41.4 intercalate into DNA, causing frameshift mutations aflatoxins

Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 15 Figure 41.5 disrupt synthesis and metabolism of sphingolipids fumonisins

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Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 17 Controlling Food Spoilage

Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 18 Removal of Microorganisms usually achieved by filtration commonly used for water, beer, wine, juices, soft drinks, and other liquids

Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 19 Low Temperature refrigeration at 5°C retards but does not stop microbial growth –microorganisms can still cause spoilage with extended spoilage –growth at temperatures below -10°C has been observed

Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 20 High Temperature canning pasteurization

Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 21 Canning food heated in special containers (retorts) to 115° C for 25 to 100 minutes kills spoilage microbes, but not necessarily all microbes in food Figure 41.6

Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 22 Spoilage of canned goods spoilage prior to canning underprocessing leakage of contaminated water into cans during cooling process

Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 23 Pasteurization kills pathogens and substantially reduces number of spoilage organisms different pasteurization procedures heat for different lengths of time –shorter heating times result in improved flavor

Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 24 Water Availability

Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 25 Chemical-Based Preservation GRAS –chemical agents “generally recognized as safe” pH of food impacts effectiveness of chemical preservative

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Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 27 Radiation ultraviolet (UV) radiation –used for surfaces of food-handling equipment –does not penetrate foods radappertization –use of ionizing radiation (gamma radiation) to extend shelf life or sterilize meat, seafoods, fruits, and vegetables –kills microbes in moist foods by producing peroxides from water peroxides oxidize cellular constituents

Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 28 Microbial Product-Based Inhibition bacteriocins –bactericidal proteins active against related species –some dissipate proton motive force of susceptible bacteria –some form pores in plasma membranes –some inhibit protein or RNA synthesis e.g., nisin –used in low-acid foods to inactivate Clostridium botulinum during canning process

Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 29 Food-Borne Diseases two primary types –food-borne infections –food intoxications

Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 30 Food-Borne Infection ingestion of microbes, followed by growth, tissue invasion, and/or release of toxins raw foods (e.g., sprouts, raspberries, and seafood) are important sources

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Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 32 Food-Borne Intoxications ingestion of toxins in foods in which microbes have grown include staphylococcal food poisoning, botulism, Clostridium perfringens food poisoning, and Bacillus cereus food poisoning

Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 33 Detection of Food-Borne Pathogens must be rapid and sensitive methods include: –culture techniques – may be too slow –immunological techniques - very sensitive –molecular techniques probes used to detect specific DNA or RNA sensitive and specific

Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 34 Figure comparison of PCR and growth for detection of Salmonella

Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 35 Figure 41.7 nucleic acid can be detected even when plaque-forming ability is lost

Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 36 Surveillance for food-borne disease PulseNet –established by Centers for Disease Control –uses pulsed-field gel electrophoresis under carefully controlled and duplicated conditions to determine distinctive DNA pattern of each bacterial pathogen –enables public health officials to link pathogens associated with disease outbreaks in different parts of the world to a specific food source

Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 37 Surveillance… FoodNet –active surveillance network used to follow nine major food-borne diseases –enables public health officials to rapidly trace the course and cause of infection in days rather than weeks

Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 38 Microbiology of Fermented Foods major fermentations used are lactic, propionic, and ethanolic fermentations

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Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 40 Fermented Milks mesophilic – Lactobacillus and Lactococcus thermophilic – Lactobacillus and Streptococcus therapeutic – Lactobacillus and Bifidobacterium yeast lactic – yeasts, lactic acid bacteria, and acetic acid bacteria mold lactic – filamentous fungi and lactic acid bacteria

Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 41 Cheese Production milk lactic acid bacteria and rennin  curd removal of whey  ripening by microbial action  cheese

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Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 43 Meat and Fish sausages hams bologna salami izushi – fish, rice, and vegetables katsuobushi – tuna

Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 44 Production of Alcoholic Beverages begins with formation of liquid containing carbohydrates in readily fermentable form –must juice from crushed grapes –mashing hydrolysis of complex carbohydrates in cereals by addition of water and heating mixture yields wort – clear liquid containing fermentable carbohydrates

Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 45 Figure racking – removes sediments or microbial oxidation of ethanol to acetic acid yields wine vinegar

Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 46 Beers and ales malt –germinated barley grains having activated enzymes mash –the malt after being mixed with water in order to hydrolyze starch to usable carbohydrates bottom yeasts –used in production of beers top yeasts –used in production of ales

Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 47 pitched Figure 41.16

Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 48 Distilled spirits similar to beer-making process –begins with sour mash mash inoculated with homolactic bacterium –following fermentation, is distilled to concentrate alcohol

Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 49 Production of Breads involves growth of Saccharomyces cerevisiae (baker’s yeast) under aerobic conditions –maximizes CO 2 production, which leavens bread other microbes used to make special breads (e.g., sourdough bread) can be spoiled by Bacillus species that produce ropiness

Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 50 Other Fermented Foods silages –fermented grass, corn, and other fresh animal feeds

Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 51 Figure Making sauerkraut

Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 52 Microorganisms as Foods and Food Amendments variety of bacteria, yeasts, and other fungi are used as animal and human food sources probiotics –microbial dietary adjuvants –microbes added to diet in order to provide health benefits beyond basic nutritive value

Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 53 Benefits of probiotics immunodilation control of diarrhea anticancer effects possible modulation of Crohn’s Disease in beef cattle, –decrease E. coli in poultry, –limit colonization of gut by the process of competitive exclusion

Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 54 Prebiotics oligosaccharide polymers that are not processed until they enter large intestine symbiotic system –combination of prebiotics and probiotics –results in production of certain acids that may be responsible for possible beneficial effects of probiotics